Ferritic stainless steel sheet is being used in a wide range of fields such as household electrical appliances or kitchen appliances and interior or external siding in building materials. In recent years, improvements in the art of refining have made much lower carbon and nitrogen contents and reduction of P, S, and other impurity elements possible. Ferritic stainless steel sheet which has been raised in corrosion resistance and workability by adding Nb, Ti, and other stabilizing elements (below, “high purity ferritic stainless steel sheet”) is being applied to a broad range of applications. This is because high purity ferritic stainless steel sheet is superior in terms of economy compared with austenitic stainless steel sheet which contains a large amount of Ni—an element whose price has remarkably soared in recent years.
In recent years, in high purity ferritic stainless steel sheet excellent in corrosion resistance, demand has been rising for an anti-glare property as one facet of the surface quality of steel sheet not only in interior and exterior siding in building materials, but also in household electrical appliances and kitchen appliances. In general, ferritic stainless steel sheet is inferior compared to austenitic stainless steel sheet in anti-glare property. Austenitic stainless steel sheet relatively easily forms intergranular corrosion grooves by nitric hydrofluoric acid pickling. Due to the random reflection of light by the microrelief shapes, it is easy to obtain surface properties excellent in milky white color and low luster anti-glare property. As opposed to this, high purity ferritic stainless steel sheet contains large amounts of at least one of Cr and No so is high in alloying degree and has Nb, Ti, etc. added as stabilizing elements. Therefore, high purity ferritic stainless steel sheet is high in intergranular corrosion resistance and is not formed with intergranular corrosion grooves in annealing and pickling. This is disadvantageous for securing an anti-glare property.
Due to the above-mentioned problems in the anti-glare property, various methods of production have been studied in recent years. For example, PLT 1 discloses a method of production of dull finish stainless steel sheet excellent in anti-glare property, color tone uniformity, and corrosion resistance comprising annealing and pickling stainless cold rolled steel sheet in the atmosphere, then lightly rolling it by dull rolls and further annealing or bright annealing, then pickling it in the atmosphere.
PLT 2 discloses a method of production of dull finish stainless steel sheet comprising, during the pickling performed before and after dull finish rolling of the sheet, prescribing in detail the conditions of electrolytic pickling by a sulfuric acid aqueous solution and nitric acid aqueous solution and conditions of dipping in a nitric hydrofluoric acid aqueous solution.
However, PLT 1 and PLT 2 disclose examples of SUS304 and SUS444 of the Japan Industrial Standard (JIS standard), but do not disclose details of the chemical composition of the steel.
As high purity ferritic stainless steel sheet, for example, PLT 3 discloses ferritic stainless steel sheet which contains Cr: 16 to 35% and Mo: less than 6% and further contains one or more of Nb: 0.01 to 1%, Ti: 0.01 to 0.5%, V: 0.01 to 0.3%, Cu: 0.5% or less, and Al: 0.005 to 0.3%, in which ferritic stainless steel sheet, the conditions of electrolytic pickling in the nitric acid aqueous solution are defined and the color tone stability anti-glare property and corrosion resistance are improved, and a method of production of the same.
PLT 4 discloses ferritic stainless steel sheet which contains C≦0.02%, N≦0.02%, Cr: 21.5 to 31%, Mo: 0.3 to 4%, Ti: 0.1 to 0.3%, and Nb: 0.15 to 0.5% and satisfies Cr+1.7Mo≧24%, in which ferritic stainless steel sheet, annealing is performed in an oxidizing atmosphere, the conditions of nitric hydrofluoric acid pickling after that are defined, and the corrosion resistance is improved, and a method of production of the same.
Further, PLT 5 discloses high Cr-content bright annealed stainless steel sheet which has a chemical composition of which satisfies C≦0.02%, Si≦1%, Mn≦1%, P≦0.04%, Ni≦0.6%, Cr: 16 to 35%, Ti: 0.05 to (0.5-10×N), Al: 0.005 to 0.3%, Mo≦0.6%, Nb≦1%, Cu≦0.5%, and N≦0.02%, in which ferritic stainless steel sheet, details of the bright annealing conditions are defined and the surface of the steel sheet is formed with relief shapes with a 10-point average roughness Rz of 1 to 50 μm, whereby an anti-glare property is imparted and the surface quality of the steel sheet is improved, and a method of production of the same.
PLTs 3 to 5 disclose examples of ferritic stainless steel sheet which contain Cr: 22% or more and Mo. Therefore, the stainless steel sheets which are disclosed in PLTs 3 to 5 relate to high purity ferritic stainless steel sheet which contains large amounts of at least one of the above-mentioned Cr and Mo.
On the other hand, as high purity ferritic stainless steel not containing large amounts of at least one of Cr and Mo, for example, PLT 6 discloses ferritic stainless steel sheet which contains C≦0.03%, Si≦0.3%, Mn≦1%, P≦0.08%, S≦0.02%, Cr: 10 to 35%, N≦0.08%, Nb: 0.05 to 2%, Ti: 0.05 to 2%, and Al: 0.08 to 0.8%, in which ferritic stainless steel sheet, a surface film which is formed by bright annealing contains Al: 15 at % or more and Nb: 6 at % or more and further Ti, a surface roughness is made an average roughness Ra of 0.3 μm to 0.95 μm to impart an anti-glare property, and the corrosion resistance and workability are improved. The ferritic stainless steel sheet of PLT 6 defines the surface film which is formed by the bright annealing so as to improve the corrosion resistance without including large amounts of at least one of Cr and Mo.
Up until now, from the viewpoints of resource-saving and workability, the inventors have proposed high purity ferritic stainless steel improved in corrosion resistance and workability without high alloying by the inclusion of at least one of Cr and Mo but by addition of a fine amount of Sn. The high purity ferritic stainless steel sheets which are proposed in PLTs 7 and 8 are high purity ferritic stainless steels which contain Cr: 13 to 22% and Sn: 0.001 to 1%, which reduce the C, N, Si, Mn, and P, have Al in 0.005 to 0.05% in range, and, in accordance with need, have stabilizing elements of at least one of Ti and Nb added.